Multi-axis machining machines have heretofore been known which machine workpieces, such as cylinder heads and cylinder blocks of engines and transmission cases, by means of a multi-axis tool called a gang head. One example of such multi-axis machining machines is disclosed in Japanese Patent Application Laid-open publication No. 2011-240466 (hereinafter referred to as “the relevant patent literature”).
As shown in FIG. 10, a machining apparatus 100 disclosed in the relevant patent literature includes a clamp unit 102 for positioning and clamping two workpieces 101, and a machining unit 103 for machining the clamped workpieces 101. The clamp unit 102 includes a vertical wall 105 projecting upward from a central portion of a turntable 104, and two workpieces 101 are clamped by two pallets 106 provided on opposite surfaces of the vertical wall 105, one workpiece 101 by each of the pallets 106. The machining unit 103 includes a plurality of multi-axis tools 108 provided on an index device 107, and the workpieces 101 clamped by the pallets 106 are machined by these multi-axis tools 108.
The workpieces 101 each have a plurality of machining surfaces (i.e., surfaces to be machined), and the turntable 104 is turned through 90 degrees as necessary to change respective angles of the workpieces 101 relative to the multi-axis tools 108, so that the plurality of machining surfaces of each of the workpieces 101 can be machined. For example, after only one of the workpiece 101 is machined, the turntable 104 is turned through 90 degrees so that respective side surfaces of the two workpieces 101 are opposed to the multi-axis tool 108, and then, the two workpieces 101 are machined concurrently.
If a plurality of workpieces 101 can be machined concurrently, an enhanced machining efficiency can be achieved. Specifically, if two workpieces 101 are placed or positioned on each of the two pallets 106, then a four workpieces can be machined concurrently, so that the machining efficiency can be enhanced.
According to the technique disclosed in the relevant patent literature, however, because the workpieces 101 are oriented vertically on the clamp unit 102, it is difficult to place or position two workpieces 101 vertically on each of the pallets 106, and thus, only up to two workpieces 101 can be machined concurrently. Further, because the workpieces 101 transferred to the clamp unit 102 in a horizontal posture by a workpiece transfer device have to be mounted on a jig (comprising the pallets 106 and the vertical wall 105) after being changed from the horizontal posture to a vertical posture, the workpiece transfer device tends to be complex in construction and costly. Thus, in order to machine different surfaces of the workpieces 101, the work pieces have to be repositioned on other different jigs, which results in a poor production efficiency or productivity. Therefore, more improvement is to be made in order to enhance the productivity.
Further, because each of the multi-axis tools 108 has a predetermined machining range, it is necessary to position many workpieces 101 within the machining range. If it is desired to simply place many, e.g. four, workpieces 101 on the turntable 104, the jig (comprising the pallets 106 and the vertical wall 105) has to be reduced in thickness in order to position all of the four workpieces 101 within the machining range. As the number of workpieces 101 increases, the number of cutting oil and air feed ports must increase. However, with the pallets 106 and the vertical wall 105 reduced in thickness, it is difficult to increase the number of cutting oil and air feed ports on the thickness-reduced pallets and vertical wall, but also it is difficult for the thickness-reduced pallets and vertical wall to have sufficient rigidity to support the four workpieces 101.